1.Field of the Invention
This invention relates to an assembly for use in recording or preserving the predetermined and critical overall length of an elongate variable length device, such as a pitch change link device for a helicopter blade. The assembly is used prior to the repair or replacement of the critical length device. This is so that, after the repair or replacement of the device, its overall length can be adjusted, if needed, so that it is equal to the original critical length before the repair or replacement of it. Such critical length devices, ordinarily, include an adjustable joint threadably connected on each end of an elongate member. The overall length of the critical length device can be adjusted by threaded movement of one or both of the joints. This invention is for use to record and preserve the critical overall length of such a device prior to a repair or a replacement of it with a repaired or replaced device. Using the assembly of this invention as a reference, the repaired or replaced device can be adjusted so that it is the same predetermined critical length it should be.
2. Description of the Prior Art
The use of pitch change links on helicopters is well known. Pitch change links determine the pitch of helicopter blades. A pitch change link is composed a member having an axially movable joint attached to each of its opposite ends. When adjusted to a precise critical length, it is utilized to set the pitch of an individual helicopter blade. The overall length of the pitch change link, including the end joints, sets or determines the precise pitch of an associated blade. There is no room for error of that overall length. It is precisely set and the length is critical. In use, the links rotate with each blade and are connected to the innermost end of each blade substantially adjacent the primary rotor for the individual blades.
The correct pitch of a blade is dependent on the length of the link. A variance in the pitch of the individual helicopter blade is of course extremely important. A change of the predetermined overall, critical length of the all important pitch change link of a blade, even as much as 0.010 inch, will result in extreme wear and fatigue of the frame and components of the helicopter. Accordingly, it is extremely important, after the initial assembling of the helicopter, that any subsequent removal of a link for a repair or replacement be followed by replacement of a link that is the same precise overall length as was the link when removed from the helicopter. By way of further explanation, in the case of a helicopter pitch change link, it is a rod with adjustable joints connected to the rod at each end. The joints are commonly known in the industry as Heim joints. Typically, such joints include a stem having, at one end, a threaded aperture in which a ball is rotatably housed, at the other end, an internally threaded recess for threaded connection to one of the ends of an elongate member or bar spanning a pair of such end joints.
Based on the critical need to maintain the overall length of each pitch change link for helicopter blades, it is important that a device be available to preserve and record the overall link length as an aid in repairing and replacing the links. To date, no such device or assemblies are available which will ensure the accurate and convenient replacement of a pitch change link from a helicopter with one which is of the same precise overall and critical length as it was prior to the removal of the link from a helicopter.